Ferromagnetic oxidic material



July 10, 1962 G. H. JoNKER 3,043,776

FERROMAGNETIC OXIDIC MATERIAL Filed April 16, 1958 3 Sheel'.s-Shee'fl 1 ..Annn\nnnnv Annnnnnnn Annnnnnnve' Fl GA Annnnn Annnnn AAnlwmvn Annnv\\\v \n Annnnn;wAnnnnnvAn vvvvv v v INVENTOR GERARD HEINDRICH JoNKER BY 2.04- ,e

AGEN

July 1o, 1962 G. H. JONKER 3,043,776

FERROMAGNETIC OXIDIC MATERIAL Filed April 16, 1958 3 Sl'xees-Shee'rl 2 FI G4 lNvENToR GERARD HEINRICH JONKER AGENT July 10, 1962 G. H. JONKER FERROMAGNETIC OXIDIC MATERIAL 5 Sheets-Sheet 3 Filed April 16, 1958 ,AVAVAVA 2o VAVAVA mmv, AvAvAvAvA AVAVAVAVNA 15 V AVN AVA AVAV AV FI G5 l ENTOR GERARD lNRICH JONKER AGENT 3,043,776 FERRGMAGNEMSC UXHDC MATERIAL Gerard Heinrich Itoniter, Eindhoven, Netherlands, as-

signor to North American Philips Company, Inc., New

York, NX., a corporation of Deiaware Filed Apr. 16, i958, Ser. No. 728,849 Claims priority, application Netherlands Apr.

il Ciaims. (Cl. 252-625) My invention relates to ferromagnetic oxidic materials, which have valuable electromagnetic properties and methods of making the same. y

More particularly, the materials according to the invention have a saturation magnetization of the same order of magnitude as that of ferromagnetic ferrites having the crystal structure of the mineral spinel, the so-called "spinel structure, and like the ferrites, most materials according to the invention have a high specific resistance. Many of them can be formed as ferromagnetic bodies for'use atr high frequencies, frequently up to 20() mc./s. and upwards.

Ferromagnetic ferrites having spinel structure, exhibit an initial permeability which is not independent of frequency, but there is afrequency range in which the initial permeability decreases with increasing frequency. This Patented .italy 10, 1962 fice . garded to be built up and from which these materials can decrease in initial permeability usually begins at a lower I frequency when the material has a higher initial permeability at low frequency (see H. G. Beljers and l. L. Snoek, Philips Technical Review, l1, pages 313-322, 1949- 1950). However, with part of the materials according to the invention, the initial permeability is constant up to a much higher frequency than with ferromagnetic ferritos having spinel structure which have the same value for the initial permeability at low frequency. Since the use of ferromagnetic cores in a frequency rangey in which the structure, the crystal anisotropy is given to a rst approximation by the expression:

FKIKl sin2\.9

(see R. Becker and W. Doring, Ferromagnetismus, 1939, page 114). If for a crystal K1 is positive (so-called positive crystal anisotropy), the hexagonal axis in this crystal is the preferential direction of magnetization. If, however, Kl is negative (in which eventrefe'rence vwill be made in this specification to negative crystal anisotropy), this means that the spontaneous magnetization is directed at right angles to the hexagonal axis and hence is parallel to the basal plane of the crystal. In the latter case, the crystal has a so-called preferred plane of magnetization. However, the possibility of the presence of a comparatively weak preference of the magnetization'for given directions in the basal plane remains.

The invention will be described with reference to the accompanying drawing, in which: i

FIG. l is a ternary phase diagram showing the compositions according to the invention;

FIG. 2 is a portion of the ternary phase diagram of FIG. 1 which shows the compositions according to the invention;

FIG. 3 is a portion of the ternary phase diagram which shows one class of compositions according to the inven- K tion;

FIG. 4 is a portion of the ternary phase diagram which Y are ferromagnetic.

be manufactured, viz. AO (in which A represents at least one of the bivalent metals Ba, Sr, Pb and Ca), Fe2O3 and MeO (in which Me represents at least one of the bivalent metals Fe, Mn, Co, Ni, Zn, Mg, Cu or the bivalent com- Plex.

.. Li++pe+++ Point 1 infFIG. 1 corresponds to the compoundAFe2O4, in which A represents at least one of the bivalent metals Ba, Sr, Pb and Ca. These compounds are not ferromagnetic.

Point 2 in FIG. 1 corresponds to the compounds with the formula MeO.Fe2O3 or MeFe2O4, in which Me represents at leastone of the bivalent metals Fe, Mn, Co, Ni, Zn, Mg, Cu or the bivalent complex These compounds have a cubic crystal structure corresponding to that of the mineral spinel, the so-called spinel structure. With the exception of ZnFe2O4, all of them Many of these materials have a high value for the initial permeability, which, however, as previously mentioned, is not independent of frequency. It is possible, for each material, to indicate a frequency range in which the initial permeability decreases with increasing frequency and this decrease begins at a lower frequency as the material has a higher value for the initial permea bility lat low frequency. It is also possible that Fe203 in a given form in the spinel lattice dissolves in an amount which is dependent upon the temperature used in the manufacture. Therefore, not only the formula but also the formula MeO.(l-[x)Fe2O3 wherein, for example, x 0.5 indicates the composition of these ferrites having spinel structure, which for this example corresponds to the line 2 3 in FIG.-1.

FIG.l 2 shows part of the diagram of FIG. l and the compositions of lthe materials according to the invention may also be represented therein. The angular points of this diagram are constituted by AFe2O4 (in which A representsat least one of the bivalent metals Ba, Sr, Pb and Ca), Fe203 and MeFeZO., (in Which Me represents at least one of the biva-len-t metals Fe, Mn, Co, Ni, Zn, Mg, Cu or vthe hivalent complex Li++pe+++ 2 AS the une z s in FIG. 1, the une 2 3 `in FIG. 2 corresponds to ferrites having spinel structure and having a composition corresponding to the formula MEO. 1 -l-x) P61203 Point 5 in FIG. 2 corresponds to the 'compounds of the bivalent metalsFe, Mn, Co, Ni, Zn, Mg or the` bivalent complex r 4Li+ 1:e+++

These kferromagnetic materials vhave a crystal structure, the elementary cell of which can be described in the hexagonal crystal system by a c-aXis of labout 32.8 A. and an 'a-axis of about 5.9 A. Part of these materials Vis built up of crystals having a preferred plane of magnetization at right langles to the hexagonal c-axis and these materials' have comparatively high values for .the

of these compounds may be regarded as derived from said compounds by substituting therein Fe+++ for at most one-half of Me in a ratio corresponding to Me:Fe++'+=1:% This corresponds to the formula Ao.(2-x)Meo.(s+1/3+)Fe2o3 in which x51. These materials are represented by the line 5.-6 Vin FIG. 2. Y

. Point 7 in FIG. 2' corresponds to the compound 2AO.2MeO.6Fe2O3 or A2M2Fe12022,`wherein A represents Ba, for at most one-half Sr, for at most one-,quarter Pb and/or for lat most one-quarter Ca, while Me represents at least one of the bivalent metals Fe, Mn, Co, Ni, Zn, Mg and Cu. These ferromagnetic materials have a rhombohedral crystal structure, the elementary cell of which can be described in the lhexagonal crystal system by a .c-axis of about 43.5 A. land `an a-axis of about 5.9 A. lAll these materials are built up of crystals having a preferred plane of magnetization at right angles to the hexagonal c-axis, and lthese materials have comparatively high'values for the initial permeability' also at vfreqencies up to 200mc./s. and higher.

Point 8 in FIG. 2 corresponds to -the compounds 3AO.2MeO.12Fe2O3 or A3Me2Fe24O41`, wherein A represents Ba, for at most 1A; partV Sr, for at most 1/s part Pb and/or for at most 1A@ part Ca, while Me represents at leas-t `one of the bivalent metals Fe, Mn, Co, Ni, Zn, Mg, Cu orithe bivalent complex Li+lFe+++ These ferromagnetic materials have a crystal structure, the elementary cell of which can be kdescribed in the hexagonal crystal system by ya c-axis of about 52.3 A. and an a-axis of `about 5.9 A.A Part of these materials is I built up of crystals having a preferred plane of magnetization at rightfangles to the hexagonal C-axfis and these materials have comparatively high values for the initial permeability also at frequencies up to 200 mc./s. and higher. Such is the case at room temperature if Me represents Co for lof at least 1A part which is, however, still slightly dependent upon the other bivalent metals, represented by Me. The crystals lof the remaining p-art of the materialshave a preferred direction of magnetiza? tion parallel to :the hexagonal c-axis. h

' Point 9 in FIG. 2 corresponds to the compounds LAOlMeQlSFez'OS or A4Me2Fe36O0, in which A represents Ba, for at most 1/s part Sr, for at most Ms part Pb Such is the case at room temperature if MeV Furthermore, there are AO.2MeO.8Fe2O3 tor AMezFelOz-l, in which A represents at yleast one of the bivalent metals Ba, Sr, Pb and for at most LVs part Ca, while Me represen-ts at least one y and/or for at most 3A0 part- Ca, while Me represents at least 'one of the bivalent metals Fe, Oo, Ni, Zn, Mg and for at most %0 part Mn or Cu. These ferromagnetic materials have a. rhombohedral crystal structure, the elementary cell of which can` be described in the hexagonal crystal system by a c-axis of about 113.1 A. and an aaxis of about 5.9 A. Part of these materials is built up i Such is the case at room temperature if Me represents Co, for at least ?/10 part, which is, however, still slightly dependent` upon the other bivalent metals represented by Me. The crystals of the other partof the materials havea preferredY direction 'of magnetization parallel to the hexagonal c-axis.

Point Y10 in FIG. 2 corresponds to the compounds 2AO.2MeO.l4Fe2O3 or A2Me2Fe28O46, in which A represents at leas-t one of the bivalent metals Ba, Sr, Pb and for at most 2/s part Ca, while Me represents at least one ofthe bivalent metals Fe, Mn, Co, Ni, Zn, Mg or the bivalent complex These ferrom-agentic materials have a rhombohedral crystal structure, the elementarycell of which can be described in the hexagonal crystal system by a c-axis of about 84.1 A. and an a-axis of about 5.9 A. Part of these materials is built up of crystals having a preferred plane of magnetization at right angles to the hexagonal c-axis and these materials have comparatively high values for the initial permeability also at frequencies up to 200 mc./s. andy upwards. Such isthe case at room temperature if Me represents Co, for at least one-half, which is, however, still slightly dependent upon the other bivalent metals represented by Me. The crystals of the other part of the materials have a preferred direction of magnetization parallel to Vthe hexagonal c-axis. Furthermore, there are compounds having the same crystal structure and corresponding ferromagnetic properties. The composition of these compounds may be regarded to be derived from the said compounds by substituting therein Fe+++ for at most one-half of Me in :a ratio corre- 2-21 mol percent of AO 5-45 mol percent of MeO 52-83 mol percent of Fe2O3v in which A represents at least one of the bivalent metals Ba, Sr, Pb and Ca and Me represents at least one of the bivalent metals Fe, Mn, Co, Ni, Zn, Mg, Cu or the bivalent complex Li++Fe+++ 2 and consist principally of at least two ferromagnetic crystal phases belonging to the `group formed by the following six members: f

The cubic crystal structure of the mineral spinel, The hexagonal crystal structure having a c-axis of about 32.8 A. and an a-axis of about 5.9 A.,

The hexagonal crystal ystructure having a c-axis of about 43.5 A. and an a-axis of about 5.9 A.,

Ihe hexagonal crystal structure having a -axis of abouty 52.3 A. and an a-axis of about 5.9 A.,

The hexagonal crystal structure having a c-axis of about 113.1 A., `and an a-'axis of about 5.9 A.,.and

The hexagonal crystal structure having a c-axis of about 84.1 A. and an a-axis of about 5.9 A. The range compromising the compositions of the materials according to 8-21 mol percent of AO 5-21 mol percent of MeO 58-83 mol percent of Fe203 The range comprising the compositions o-f thesematen'als is shown in FIG. 2.

'The crystals of the above-mentioned hexagonal crys-` tal phases have either a preferred plane of magnetization at right angles to the hexagonal c-axis or a preferred direction of magnetization .parallel to the hexagonal c-axis. In order to determine whether in a given case crystals having a preferred plane of magnetization or crystals having a preferred direction of the magnetization are concerned, the following identification test, for example, may

serve:

A small amount, for example, 25 mgs., of the material to be tested, in the form of a finely lground powder, is mixed with a few drops of -a solution of an organic binder or adhesive in acetone, which mixture isy spread on a glass slide. This slide is arranged between the poles of an electromagnet so that the lines of magnetic force are at right angles to the surface of the slide. By slowly increasing the electric direct current of the electromagnet, the magnetic field strength is increased so that the particles of the powder rotate in the field in `a manner, such that either the preferred direction or lthe preferred plane of magnetization becomes approximately parallel to the direction of the lines of magnetic force. By proceeding carefully, it is possible to prevent the powder particles from coagulation. After the acetone has evaporated, the powder particles keep adhering to the glass surface in the magnetically oriented condition. By means of radiographs, it is then possible to determine which orientation of the powder particles has been produced by the action of the magnetic field. This can be effectedA inter'alia with the aid of Ian X-ray ditfractometer (for example, an apparatus as described in Philips Technical Review, 16, pages 12S-133, 1954-55), wherein in the case of ya preferred direction parallel to the hexagonal c-axis one observes as intensified occurrence of the reections at planes at right `angles to this c-axis (so-called 00l-reections) in comparison with a radiograph of a non-oriented preparation. vIn the case of a preferred plane at rightangles to the 'hexagonal c-axis, `one observes an intensified occurrence of reflections at planes parallel to this c-aXis (socalled hk0-reflections).

It will be evident that the materials according to the invention may contain at the same time hexagonal crystal phases having a preferred plane of magnetization at right angles to the hexagonal c-axis and hexagonal crystal phases having .a preferred direction of magnetization parallel to the hexagonal c-axis. However, since the physical properties of the materials are greatly dependent upon the kind of the preference of the magnetization, those materials according to the invention are preferable which have the same crystal anisotropy with regard tothe hex-agonal crystal phases. Those materials according to the invention, the hexagonal crystal phases of which have a preferred plane of magnetization at right angles to the hexagonal c-axis, have `an initial permeability which is constant to a much higher frequency than with ferromagnetic ferrites having spinel structure which have the Same value for the initial permeability at low frequency. Those materials :according to the invention, the hexagonal crystal phases of which have a preferred direction of magnetization parallel to the hexagonal c-axis, afford new possibilities for the manufacture, for example, of `ferromagnetic bodies having permanent magnetic properties and ferromagnetic bodies for use inmicro-wave equipment.

The ferromagnetic compounds having a cubic Vcrystal structure corresponding to that of the mineral spinel are substantially all important on laccount of their value for the initial permeability. Oonsequently, in a physical sense, they are more similar to the above-mentioned hexagonal crystal phases having a preferred plane of magnetization than to the above-mentioned hexagonal crystal phases having apreferred direction` of magnetization. Consequently, of the materials according to the invention, in which the cubic crystal phase having a structure of that of the mineral spinel is present, those are preferable which contain hexagonal crystal phases having a preferred plane of magnetization. Ferromagnetic compounds having the cubic spinel structure, are preferrred for which the losses at the frequency at which the material is useable because of the properties of the hexagonal crystal phases, has not increased to a high value. Those compounds are ones which have a comparatively low value for the initial permeability at low frequency.

The hexagonal crystal phases of the materials according to the invention have a preferred plane of the magnetization at room temperature if these materials are of the following composition:

2-21 mol percent of AO.

x mol percent of CoO 0-(45-x) mol percent of MeO 52-83 mol percent of Fe203k wherein 7g x 45. This range of compositions is shown in FIG. 3, which represents the same diagram as FIG. 2.

The materials according to the inventionhaving a cornposition `corresponding to 8-21 mol percent of AO y mol percentof COO 0-(21-y) mol percent of Me() 58-83 mol percent of Fe203 wherein 7y2l, contain substantially hexagonal crystal` l 15 to 2l mol percent of AO z mol percent :of CoO 4 to (2l-z) mol pencent of MeO 58 to'78 mol percent of Fe203 wherein 322g 17. These materials contain substantially hexagonal crystal phases. This range of compositions is represented in FIG. 4, which shows the same diagnam t as FIG. 2.

Finally, a preferred plane of the magnetization at room temperature occurs in the hexagonal crystal phases of materials according to the invention having a composition corresponding to 18-45 mol percent of AO 18-45 mol percent of MeO 52-61 ino-l percent of Fe203 'Ihis range of compositions is represented in FIG. 5, which shows the same 'diagnam as FIG. 2.

A preferred direction of magnetization at room temperature occurs in the hexagonal crystal phases of ma- FIG. 5.

' the bivalent metals Fe, Mn, Ni, Zn, Mg, Cuor the bivalent Vcomplex impe-n Y '2 These materials contain substantialy hexagonal crystal phases.V This range of compositions is represented in The hexagonal crystal phases of the materials according to the invention :also have la preferred direction of the Y magnetization at room temperature if-these material-s are of Ithe following composition:

8-13 mol percent of AO b mol percent of CoO (c-b) mol percent of DO 169-83 mol percent of Fe203 wherein b, c20 and (c-b)0. In this case also D represents at least one of the bivalent metals Fe, Mn,

Mi,jZ n, Mg, Cu or the bivalent complex LLi++1= These materialscontain substantialy hexagonal crystal phases. This range of compositions isrepresented in FIG. 4. Y

. The lmaterials Kaccording to the invention are manufacturedby heatingtsintering) a finely-divided mixture of the component meta-l oxides of the materials chosen approximately in `the correct proportion, It is, ofcourse, possible for one or more ofthe constituent metal oxides to vbe replaced wholly or in part by compounds converting into metal oxides upon heating, for example, carbonates, oxalates :and aCetateS. Furthermore, the component metal-oxides may be replaced Wholly or in part by one or more compounds .ofwat least one of the component metal oxides, for example, BaFemOlg. The term correct proportion is to be understood in this case to mean Ea ratio of the amounts of metals in the initial mix- Y tureV equal to that in the materials to be manufactured in the manufacture of ferromagnetic ferrites with spinel structure (inter alia I. I. Went and E. W. Gorter, Philips Technical Review, 13 page 183, 1951-1952). The temperature of the sintering process or the nal sintering process is chosen between about 1000ov C. and about 1450'c C. and preferably between 1200 C. and 1350 C.

In order to facilitate the sintering process, it is possible -to add sintering agents, such as silicates and fluorides. Bodies, consisting of the ferromagnetic materials previously `described may be obtained by sinterng the initial mixture of the metal oxides or the like right from the beginning inthe desired form' and Aalso by pulverizing-.the reaction product of `the presintering process, giving it the desired shape, if .desired `after the addition of a binder, which may -be followed by 1a subsequent -sintering or hardening treatment.

Sintering at a temperature considenably higher than 1200 C. land/or sintering in .a gaseous atmosphere compar-atively poor in` oxygen results in a material having a comparatively high Fe++ content, so that the specific repounds, the materials according to the invention have the sistance may bedecreased to values lower than 10Q-cm. If lthis is not desired, because the material is intended to be used as an .initial material for magnetic cores'at high frequencies without being hindered by eddy-current losses, then either undue productionV of ferrous ionsmust be avoided or ferrous ions produced in excessive quantity must be oxidized afterwards in known manner to form ferrie ions, for example, by subsequent heating in oxygen 'at a temperature between 1000 C. and 1250 C.

With respect to the above-described monophase comadvantage that their initial mixtures maybe sintered to greater density more readily than inthe manufacture of the Iaforementioned mon-ophase compounds. This greater density, which is conducive to the obtainment of a higher value for the magnetization per unit volume .and also for the initial permeability, may thus be obtained at a lower temperature in the manu-facture of the materials according to the invention, which is ladvantageous since a smaller Fe++ content is thus produced ythan with sintering .at a higher temperature. e The electromagnetic losses 'are indicated, as is common practice, by a loss factor (see J. Smit and H. P. I. Wijn Advances in Electronics, VI, 1954, page 69, Formula No. 37). The magnitude ,Lt is the so-called real part ofthe initial permeability. The magnitude u" is the so-called .induction component of the initial permeability.

EXAMPLE I A mixture consisting of barium carbonate, zinc oxide and ferric oxide in a ratio at 17.6 mol percent of BaO, 11.8 mol percent of ZnO and 70.6 mol percent of Fe203, which corresponds to the compound Ba3Zn2Fe24O41, was mixed with ethyl alcohol in a ball 'mill for l hour and subsequently presintered at 1000 C. in air for 15 hours. The reaction product was ground with ethyl alcohol in a ball mill for 1 hour. Subsequently, after drying, part of the product, to which a small amount of an organic binder had been added, -was pressed to form rings. These rings were sintered in oxygen atV 1200 C. Vfor 2 hours. The density of these rings Was 3.57 g./cm.3. The remaining part ofthe product was presintered at 1000 C. and ground, was again presintered in air at 1200 C. for 2 hours. This reaction productwas ground with ethylalcoy hol in a ball mill for 11/2 hours and subsequently, after drying, the product, to which a small amount of an organic binder had been added, was pressed to form rings which Were sintered in oxygen at 1260? C. for 2 hours. The density of these rings was 3.73 g./crn.3 An X-ray examination revealed that all rings consisted of crystals, the elementary cell of which can be described in the hexagonal crystal system by a c-axis of about 52.3 A. and an a-axis of about 5.9 A.

In a similar manner, rings were manufactured from an initial mixture corresponding to .18.1 mol percent of BaO, 13.8 mol percent of ZnO and 68.1 mol percent of Fe203. The rings were sintered at 1200 C. and had a density of 3.92 g./cm.3. The density ofthe rings sintered at 1260" C. at 4.06 g./cm.3. An X-ray examination reveals that all these rings contain two hexagonal crystal phases, one, the principal, having a c-axis of about v52.3 A. and an a-axis of about y5.9 A., and a second, present in small quantity, having a c-axis of about 43.5 A. and an a-axis of about 5 .9 A.

EXAMPLE II A mixture consisting of barium carbonate, cobalt carbonate and ferric oxide in a ratio of 17.6 mol percent of BaO, 11.8 mol percent of CoO and 70.6 mol percent of Fe203 which corresponds to the compound Ba3Co2Fe24O41 was presintered twice in the manner indicated in Example 9 10 t I and pressed intol rings. These rings where sintered in `in the"hexa'gonal crystal system by a '-axis of about 32.8 oxygen at 1220 C. for 2 hours. The density of these A. and an a-axis of about 5.9 A. y rings was 4.14 g./cm.3. An X-ray examination' revealed In a similar manner, rings were .manufactured from that the rings consisted ofcrystals, the elementary cell initial mixtures correspondirigto of which can be described in the hexagonal crystal system by a c-axis of about 52.3 A. and an a-axis of about 5.9 A. In a similar manner, rings were manufactured `from an initial mixture corresponding to 18.1 mol percent of BaO, 13.8 mol percent of ZnO and 68.1 mol vpercent of Fe2O3. The density of these rings was 5.25 g./cm.3 and, 10 `according to an X-ray exam-ination, the rings were found rto contain two hexagonal crystal phases, one, theprincipal, having a c-axis of about 52.3 A. and an a-axis of CID-3 and 4-6 g/Cm-3. lSPeCVelY- A11 X-fay examina* about 5 9 A and another, .present in small quantity, tion revealed that all of the rings contained two hexagonal having a c-axis of about 43.5 A. and an a-axis of about 15 crystal phases. One/.the principal. having a c-aXiS Of about inol percent. of Zn() and 78.6 mol percent of Fe203, 12.0 mol percent of BaO, 9.0 -mol percent of CoO, 3.0 mol percent of ZnO and 76.0 mol percent of Fe203,

The densities of these rings were 3.8 g./om.3, 5.0 g./

5,9 A 32.8 A. and an a-axis of about 5.9 A. and another, present EXAMPLE V111' in small quantity, having a c-axi's of about 43.5 A. and an A mixture consisting of 33 gms. of BaFe12O19, 2.67 anaxls of about 5'9 'A' v gms. of BaCO3 and 3.19 gms. of CoCO3, which mixture 20'. EXAMPLE contains the metals in quantities corresponding to 17.2 molrpercent of BaO, 12.2 mol percent of CoO and 70.6 mol percent of Fe203 (or about the compound Ba3Co2Fe24O41) was ground with ethyl alcohol in a ball carbonate and ferric oxide in ratios of mm for 1hour and Subsequently after drying the Prod" 25 18.5 mol percent of BaO, 14.8 mol` percent of ZnO and uct, to which `a small amount of an organic binder had 66] m01 percent of F6203, been @dded Was pressed to fofm Hugs'. These Hugs 18.5 mol percent of BaO, 11.1 mol-percent of Zn'O, 3.7 mol were. sintered in .oxygen at 1250 C: for 2 hours. kThe pert of COO-nd 66.7 m01 perntf F6203, denslty 0f thse flugs Was 4;()9 g-/Cm; An X'fay examl' 18.5 mol" percent of BaO, 7.4 mol percent or' ZnO, 7.4 nation revealed tbat'the rings consisted'of crystals, -the 30 m01 percent of C00. yand 667 m01 percent of F6203 elementary cell of whiohcan be described inthe hexagonal 185 m01 percent of Bao, 3.7 m01.y percent of ZDO,-11 1 crystal `system by a c-axis of about 52.3 A. and an a-axis m01 percent of COO and 667.11101 percent of F6203, Qfaii)iiustirSriigla/i.manner rings were manufactured from an 1&5 m01 prcem of Bao 14'8 m01 'percent of COO and initial mixture consisting of 33 gms. o-f BaFelgOlg.- 2.96 66'7 m01 percent .of F6203' gms. of BaCO3 and 3.50 gms. of C0003 (17.4 mol percent of BaO, 13.1 mol percent of CoO and 69.5 mol percent of Fe203). The density of these rings was 4.45 4 v v g./cm.3. The density Was 4.59 g./cm.3 for rings manu- Rings were manufactured in an analogous manner from factured from a mixture of 33 gm. of BaFelZOlg, 3.56 gms. o a mixtureconsisting of 33 gms. of BaFelZOlg, 3.3 gms. of BaCO3 and 4.12 gms. of CoCO3 (17.9 mol percent of B-aCO3, 1.5 jgmsrof ZnO and 1.94 gms. of CoCOs, 0f BaO, 14.9 m01 percent 0f COO and 67,2 m01 percent `Wl'iCh corresponds t0 17.8 m01 peCentvOf BaO, 6.8 m01 of FeZOS). An X-ray examination revealed that all the percent of ZnO, 7.2 m01 Percent 0f C0CO3 yand 68.2 m01 rings of the last two groups contained two hexagonal percent of Fe203. An X-ray'examinau'on revealed that crystal phases, one, the principal, having a c-axis of about 45 all rings contained two hexagonal crystal phases, one 52,3 A, and an a-axis 0f about 5,9 A, and another, preshaving ia c-iaxis `orf about 52.3 A. 'and ian a-axi-s of about ent in small quantity, having a c-axis of about 43.5 A. 5.9 A. `and another having a cfaxis of about 43.5 A. and and an d axis 0f about 5 9 A, an a-axis of about 5.9 A. while in the manner abovedescribed, it was also determined that, except in the ist EXAMPE IV l 50. preparation, both hexagonal crystal phases have a pre- Rings were manufactured, in the manner indicated 1n ferred plane of magnetization at right angles to the Example I, from a mixture consisting of barium carhexagonal caxis. bonate, cobalt carbonate, zinc oxide and ferric oxide, in Properties of theserings are specified inTable 1.

Rings were manufactured, in the manner indicated in presint'crin'g process took place in air at 1000 C. for 15'hoursand the rings were sintered in oxygen at 1250" C. for 2 hours. Y

Table l Composition, mol percent 80 mc./s. 160 inc./s. 260 mc./s. 5200 nio/s. 10 mld/s f r BaO ZnO C00 F6203 ,u tan y tan u tan Il tan 18. 66. 7 10. 0 6. 8 O. 26 6. 0 0. 32 5. 5 0. 41 4. 0 0. 70 18. 3 7 56. 7 6. 7 5. 8 0. 09 5. 7 0. 19 5. 7 0. 30 4. 5 0. 51. 18. 7 4 66. 7 18. 7 15. 8 O. 13 16. 1 0. 25 16. 2 0. 33 8. 8 0. 90 18. l1 1 66. 7 12. 2 11. 2 0. 07 1l. 0 0. 18 11. 1 0. 29` 8. 9v 0. 64 18. 14 8 66. 7 11. 4 8. 6 0. O2 8. 5 0. 05 9. 0 0. 16 9. 7 0. 32 17. 7 2 68. 2 12. 2 11. 0 O. 03 8. 9 0. 70

a ratio of 9.7 mol percent of BaO, v7.3 mol percentof EXAMPLE VI CoO, 2.4 mol percent of ZnO` and 80.6 mol percent of FezOs, which corresponds to the compound The rings were sintered in oxygen at 1320 C. for 2 hours. The density of the rings was 3.3 g./cm.3. An X-ray examination revealed Ethat the rings consisted of crystals, the elementary cell of which can be described 75 .Rings were manufactured in the manner indicated in 70 Example I, from mixtures consisting of Ibarium carbonate, cobalt carbonate, zinc oxide and ferrie oxide in ratios corresponding to 15.1 mol percent of BaO, 8.4 mol percent of CoO, 8.4 mol percent of ZnO and 68.1 mol percent of FezOa, respectively,

1.0.7 mol percent of BaO, 8.0Amol percent of CoO, 2.7

13.7 mol percent of BaO, 10.2 mol percent of CoO, 3.4 mol percent of ZnO and 72.7 mol percent of Fe2O3. A

Example I from ybarium carbonate, zinc ox'ide, cobaltl 13 having a c-axis of about 43.5 A. and an a-axis of about 5.9 A.

`It was determined in the above-described manner that all hexagonal crystal phases which occur in this example in which a has. a value up to 1.0, b has a value up to 0.7, c has a value up to V0.6, Me is a bivalent ion selected from the group consisting of Fe++, Co++, -Ni++, Zn++, Mg++, R is a bivalent ion selected from the group conhave a referred lane of magnetization at right ang-les h to the hxagonal axis 5 sistmg of Mn++ and Cu++, d has a val-ue up to 0.6, sa1d Properties of these rings are specified in Table 3. crystals havlng a rhombohedral structure with a c-axls 1n Table 3 Composition, Mol Percent Sintering 80 mc./s. 260 mc./s. 500 M'Hs Temp., c./ A C. S. p.' I BaO C00 ZnO Fe2O3 p tan p tan p tan k While l'I have described my invention in connection with specific embodiments and applications, other modifications thereof will be readily apparent to those skilled in this art without departing from the spirit and scope of the invention as described in the appended claims.

What is claimed is:

1. A ferromagnetic material having a composition corresponding to about 2 to 21 mol percent of AO, 5 to 45% of MeO, and about 52 to 83% of Fe2O3 in which A is a metal selected from the group consisting of barium, strontium, lead and calcium, and Me is a bivalent ion selected from the group consisting of Fedra, Mn++, Co++, Ni++, Zn++, Mg++, Cu++, and the bival'ent complex and consisting essentially of at least two crystal phases selected from the group of compositions consisting of:

A. Crystals having the composition A1 yCayMe2Fe16HIO27 in which y has a value Iup to 0.4, A is a bivalent ion selected from the group consisting of Ba++, Sr++, and Pb++, and Me is a bivalent ion selected from the group consisting of Fe++, Mn++, Co++, Ni++, Zut-t, Mg++, and the bivalent metal complex Li++Fe+++ 2 said crystals having a c-axis of 32.8 A. and an a-axis of 5.9 A. in the hexagonal system;

B. Crystals having the composition Ba(1 5l b c)SraPbbCacM2Fe2nIO22 in which a has a value up to 0.5, b has a value up to 0.25, and c has a value up to 0.25, Me is a bivalent ion selected from the group consisting of Fe++, M11-H', Co++, Ni++, Zn++, Mg++, and Cu++, said crystals having a rhombohedral structure with a c-axis in the hexagonal system of about 43.5 A. and an a-axis of about 5.9 A.

C. Crystals having the composition:

Ba3 a b GSI'aPbbCanMe2Fe24IHO41 in which a has a value up to 1, b has a value up to 0.6, and c has a value up to 0.3, Me is a bivalent ion selected fromV the group Fe+ Mn++, Co++, Ni++, Zn++, Mg'H', Cu++, and the bivalent complex Li++pe+++ 2 said crystals having a c-axis of about 52.3 A. and an a-axis of about 5.9 A. in the hexagonal system; n

D. Crystals having the composition:

the hexagonal system of about 113.1 A. and an a-axis of about 5.9 A.;

E. Crystals having the composition in which a has a value up to 0.4, Me is a bivalent ion selected from the'group consisting of Fe++, Mn++, Co++, Ni++, Zn++, Mg++, and the bivalent complex said crystals having a rhombohedral structure with a c-axis in the hexagonal system of about 84.1 A. and an a-axis of about 5.9 A.

2. A ferromagnetic material as defined in claim 1 in which the material is the tired reaction product of about 8 to 21 mol percent of AO, about 5 to 21 mol percent of MeO, and about V58 to 83 mol percent of Fe203.

3. A ferromagnetic material as defined in claim 1 in Which at least one of the hexagonal/crystal phases constituting the material has a preferred plane of magnetization.

4. A ferromagnetic material as defined in claim 2 in which at least one of the hexagonal phases constituting the material has a preferred plane of magnetization. v

5. A ferromagnetic material as defined in claim 2 in which at least one of the hexagonal crystal phases constituting the material has a preferred direction of magnetization.

6. A ferromagnetic material as defined in claim 3 in which the material is the fired reaction product of about 2 to 21 mol percent of AO, about x mol percent of CoO, up to about (45-x) mol percent of MeO, and about 52 to 83 mol percent of -Fe203, wherein x has a value of at least 7 and not more than 45.

7. A ferromagnetic material as defined in claim 3 in which the material is the fired reaction product of 2 to 21 mol percent of AO, 18 to 45 mol percent of MeO, about 52 to 61 mol percent of Fe2O3.

8. A ferromagnetic material as defined in claim 4 in which the material is the fired reaction product of about 8 to 21 mol percent of AO, about y mol percent of CoO, up to (2l-y) mol percent of MeO', and about 58 to 83 mol percent of Fe203, wherein y is at least 7 and not more than 21.

9. A ferromagnetic material as defined in claim 4 in which the material is the fired reaction product of about 15 to 21 mol percent of AO, z mol percent of C00, 4 to (2l-z) mol percent of MeO, and about 58 to 78 mol percent of Fe203, wherein z is at least 3 and not more than 17.

10. A ferromagnetic material as defined in claim 5 in which the material is the fired reaction product of about 15 8 to 19 mol percentV of AO, a m01 percent of C00-, (5-a) to (2O-a) m01 percent of DO, and 69 -to 83 mol percent of Fe203, wherein a is at least-5 and D is a'bivalent ion yselected from the group consisting of Fe++, Mn++, Ni++,

Where b is not-greater than 6.5, c Vis not less than 6.5 and not more than 20, and (c-b) is not less than zero.

References Cited in the le of this patent `UNITED STATES PATENTS 2,640,813 Berge .June 2, 1953 '2,659,698 Berge Nov. 17, 1953 2,715,109 Albers-Schoenberg Aug. 9, 1955 16 Harvey Nov. 8, 1955 Crowley et al Feb. 28,A l1956 Crowley Jan. 22, 1957 Bergman t Aug, 12, 1958 'Eckert' Mar. 10, 1959 Jonker et al. July 26, 1960 Jonker et al. July 26, 1960 Jonker et al. Oct. 4, 1960 FOREJGN PATENTS Germany Oct. 20, 1952 Germany May 2, 1955 Germany ,-Mar. 14, 1957 Great Britain Aug. 8, '1956 vGreat Britain June 12 1957 France Mar. 3,'1954 France Apr. 13,1955

OTHER REFERENCES Jonker et a1.: Philips Tech. Rev., November 30, 1956,

20 pp. 145453.v 

1. A FERROMAGNETIC MATERIAL HAVING A COMPOSITION CORRESPONDING TO ABOUT 2 TO 21 MOL PERCENT OF AO, 5 TO 45% OF MEO, AND ABOUT 52 TO 83% OF FE2O3 IN WHICH A IS A METAL SELECTED FROM THE GROUP CONSISTING OF BARIUM, STRONTIUM, LEAD AND CALCIUM, AND ME IS A BIVALENT ION SELECTED FROM THE GROUP CONSISTING OF FE++M, MN++, CO++, NI++, ZN++, MG++, CU++, AND THE BIVALENT COMPLEX 